Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
In an image reading apparatus such as a scanner and a copier, an illumination device is mounted. The illumination device irradiates a light to a document for optically reading the image of the document placed on a reading surface. Nowadays, as a light source for this illumination device, a light emitting diode (LED) is used. The LED has an advantage of high luminous efficiency. In this illumination device, it is necessary to illuminate the document in a line shape. However, since the LED is a point light source, a bar-shaped light guiding body and the LED are combined to generate a line-shaped illuminating light. The light guiding body includes an incident surface and a strip-shaped emission surface. The incident surface is arranged in an end portion of the light guiding body, and receives the illuminating light emitted from the LED. The emission surface extends along the longitudinal direction of the light guiding body, and causes emission of the illuminating light.
There is a technique that includes one light guiding body and a reflective plate disposed to extend parallel to the light guiding body, in order to illuminate the document. The light guiding body includes two emission surfaces. The light emitted from one emission surface is directly irradiated to the document. The light emitted from the other emission surface is reflected at the reflective plate, and then irradiated to the document sheet. As a result, the lights from the two directions intersecting with each other are irradiated to the document.